Wireless device, a radio node, and methods therein

ABSTRACT

A wireless device  108  and a method therein for assisting in precoder selection for wireless communication with a Radio Node (RN)  106 , and a RN  106  for performing precoder selection for wireless communication with a wireless device  108 . The wireless device is configured with a set of precoders. The wireless device determines a subset of precoders out of the set of precoders; and transmits, to the RN, at least one Sounding Reference Signal (SRS) precoded with a respective at least one precoder comprised in the subset. The RN receives, from the wireless device, at least one SRS precoded with a respective at least one precoder comprised in a subset of precoders; and transmits, to the wireless device, a signal indicative of a selected precoder to be used for a transmission to the RN, wherein the selected precoder is indirectly selected based on the received at least one SRS.

TECHNICAL FIELD

Embodiments herein relate generally to a wireless device, a radio nodeand to methods therein. In particular they relate to precoder selectionfor wireless communication.

BACKGROUND

Communication devices such as terminals are also known as e.g. UserEquipments (UE), mobile terminals, wireless devices, wireless terminalsand/or mobile stations. Terminals are enabled to communicate wirelesslyin a wireless communications network and/or cellular communicationsystem, sometimes also referred to as a cellular radio system orcellular network. The communication may be performed e.g. between twoterminals, between a terminal and a regular telephone and/or between aterminal and a server via a Radio Access Network (RAN) and possibly oneor more core networks, comprised within the wireless communicationsnetwork.

Terminals may further be referred to as mobile telephones, cellulartelephones, laptops, or surf plates with wireless capability, just tomention some further examples. The terminals in the present context maybe, for example, portable, pocket-storable, hand-held,computer-comprised, or vehicle-mounted mobile devices, enabled tocommunicate voice and/or data, via the RAN, with another entity, such asanother terminal or a server.

The cellular communications network covers a geographical area which isdivided into cell areas, wherein each cell area is served by a radionode such as a base station, e.g. a Radio Base Station (RBS), whichsometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”,or BTS (Base Transceiver Station), depending on the technology andterminology used. The base stations may be of different classes such ase.g. macro eNodeB, home eNodeB or pico base station, based ontransmission power and thereby also cell size. A cell is thegeographical area where radio coverage is provided by the base stationat a base station site. One base station, situated at the base stationsite, may serve one or several cells. Further, each base station maysupport one or several communication technologies. The base stations orradio nodes communicate over the air interface operating on radiofrequencies with the communication devices, also denoted wirelessdevices, within range of the base stations or radio nodes. In thecontext of this disclosure, the expression Downlink (DL) is used for thetransmission path from the radio node, e.g. a base station, to thewireless device. The expression Uplink (UL) is used for the transmissionpath in the opposite direction i.e. from the wireless device to theradio node. The radio node may in some circumstances, e.g. in systemsenabling device-to-device communications, also be another wirelessdevice.

Antenna beamforming is a technique of shaping the transmit radiatedenergy pattern or the receive sensed energy pattern into beams by theuse of an antenna element array. The antenna elements are typicallyclosely spaced with for example respect to the wavelength, orequivalently to the carrier frequency used for the wirelesscommunication, e.g. the radio communication. These beams may be used toconcentrate the transmitted signal energy and/or received signal energyand/or steer it in specific directions. FIG. 1 depicts a classic examplewherein a linear antenna array is used to steer the beam an angle ωoff-axis compared to the orientation of the antenna array. In order forthe waveforms from two antenna elements to superimpose constructively inthat direction, the phase rotation difference of the two signals due tothe path distance difference Δ must correspond to an integer multiple of2π. This requirement leads to an expression for the phase angle or phasedelay φ that is a function of a steering angle, an array elementdistance, and a wavelength.

FIG. 1 schematically illustrates basic beamforming using aone-dimensional linear array, wherein d is the array element distance, ωthe desired beam steering angle,

$\varphi = \frac{2{{d} \cdot {\sin(\omega)}}}{\lambda}$

the required phase delay, and λ is the wavelength. Typically d˜N2.

When used herein the term ‘beam’ is used to refer to a certain spatialtransmit radiation pattern or spatial receive sensitivity patterncreated by using a combination of multiple antenna elements and thecorresponding complex-valued weights applied to the signal at eachantenna element. Further, in this description, the transmit radiatedenergy pattern and the spatial transmit radiation pattern may also bereferred to as a transmission pattern, and the receive sensed energypattern and the spatial receive sensitivity pattern may also be referredto as a reception pattern.

One example of creating such patterns is the classical beamforming casewith a linear array with equally spaced antenna elements as depicted inFIG. 1 but other examples exist as well. In the general case, each beamcorresponds to a certain combination of complex-valued weights, alsodenoted complex antenna weights, used to transmit or receive a signal.

If there are N antenna elements, then a precoding weight vector, orbeamforming vector, is obtained as the N complex-valued weights, one foreach antenna element. A precoding weight vector is also simply referredto as a precoder. The set of possible precoders that may be used, e.g.the set of possible precoders defined in the system or in the standardspecification, is sometimes referred to as the precoder codebookalthough the term beam or beam codebook may also be used. Furthermore,in the general case, there is no need for the antenna elements to belinearly arranged with λ/2 spacing as in FIG. 1.

In case of spatial multiplexing, multiple spatial streams or layers maybe superimposed by transmitting a linear combination of the layers fromeach antenna element. The linear combination is given by a precodingmatrix which is formed by a set of precoding weight vectors, alsodenoted precoding vectors, one vector per layer.

Uplink data transmissions are scheduled by the network in LTE as well asin many other standards. The network in that case instructs the wirelessdevice to transmit in the uplink using a certain set of parameters, suchas a modulation scheme, a coding rate, a set of time-frequencyresources, and a transmit power, etc. In case of uplink beamforming, thebeam direction, or precoding weight vector, to use is provided by the 20network. Thus, the codebook is of finite size and the network may referto a specific entry of N precoding weights in the precoding codebook.

The design of the precoder codebook is done assuming a certain antennaarrangement, for example the linear and equally spaced arrangement asschematically illustrated in FIG. 1 wherein also omni-directional andidentical antenna elements may be assumed. Although such a codebook mostlikely is a good choice for the setup for which it is designed, it maynot be a good choice for other arbitrary antenna arrangements. Hence,either the antenna arrangement for which the codebook is designed needsto be mandated in all wireless devices, e.g. UEs, which significantlyrestricts the freedom of implementation, or the codebook needs to be acompromise 30 between all relevant antenna arrangements, which may limitperformance gain of using beamforming, or alternatively the number ofprecoder entries in the codebook becomes unmanageably large to supportthe large number of possible different antenna arrangements.

SUMMARY

As the state of the art requires the communication network, e.g. a radionode (RN), to have knowledge about the precoding codebook whenscheduling uplink transmissions for a wireless device, the network hasto have knowledge about the antenna arrangement of the wireless deviceor the antenna arrangement for which the codebook is designed needs tobe mandated in all wireless devices which significantly restricts thefreedom of implementation. Alternatively, and as mentioned above, thecodebook is a compromise between all the possible antenna arrangements,which limits performance gain of using beamforming. Therefore, an objectof embodiments herein is to provide a way of improving the performancein a wireless communications network, wherein the freedom ofimplementation and the performance gain of using beamforming areimproved.

According to a first aspect of embodiments herein, the object isachieved by a method performed by a wireless device for assisting inprecoder selection for wireless 15 communication with a Radio Node (RN).The wireless device is configured with a set of precoders.

In the method, the wireless device determines a subset of precoders outof the set of precoders, and transmits, to the RN, at least one soundingreference signal precoded with a respective at least one precodercomprised in the subset.

According to a second aspect of embodiments herein, the object isachieved by a wireless device for assisting in precoder selection forwireless communication with a RN. The wireless device is configured witha set of precoders. The wireless device is configured to determine asubset of precoders out of the set of precoders, and to transmit, to theRN, at least one sounding reference signal precoded with a respective atleast one precoder comprised in the subset.

According to a third aspect of embodiments herein, the object isachieved by a method performed by a wireless device for transmittingdata to a RN. The wireless device is configured with a set of precoders,wherein each precoder in the set of precoders is defined to provide arespective transmission pattern when applied to transmission on a set ofantenna elements of the wireless device.

In the method, the wireless device determines a subset of precoders outof the set of precoders.

Further, the wireless device transmits, to the RN, at least one soundingreference signal precoded with a respective at least one precodercomprised in the subset.

Furthermore, the wireless device receives, from the RN, a schedulinggrant for transmitting data, which scheduling grant is based on thetransmitted at least one sounding reference signal.

Yet further, the wireless device transmits data to the RN in accordancewith the scheduling grant.

According to a fourth aspect of embodiments herein, the object isachieved by a wireless device for transmitting data to a RN. Thewireless device is configured with a set of precoders, wherein eachprecoder in the set of precoders is defined to provide a respectivetransmission pattern when applied to transmission on a set of antennaelements of the wireless device.

The wireless device is configured to determine a subset of precoders outof the set of precoders.

Further, the wireless device is configured to transmit, to the RN, atleast one sounding reference signal precoded with a respective at leastone precoder comprised in the subset.

Furthermore, the wireless device is configured to receive, from the RN,a scheduling grant for transmitting data, which scheduling grant isbased on the transmitted at least one sounding reference signal.

Yet further, the wireless device is configured to transmit data to theRN in accordance with the scheduling grant.

According to a fifth aspect of embodiments herein, the object isachieved by a method performed by a Radio Node (RN) for performingprecoder selection for wireless communication with a wireless device.The wireless device is configured with a set of precoders.

In the method, the RN receives, from the wireless device, at least onesounding reference signal precoded with a respective at least oneprecoder comprised in a subset of precoders out of the set of precoders.

Further, the RN transmits, to the wireless device, a signal indicativeof a selected precoder to be used for a transmission to the RN, whereinthe selected precoder is indirectly selected based on the received atleast one sounding reference signal.

According to a sixth aspect of embodiments herein, the object isachieved by a RN for performing precoder selection for wirelesscommunication with a wireless device. The wireless device is configuredwith a set of precoders.

The RN is configured to receive, from the wireless device, at least onesounding reference signal precoded with a respective at least oneprecoder comprised in a subset of precoders out of the set of precoders.

Further, the RN is configured to transmit, to the wireless device, asignal indicative of a selected precoder to be used for a transmissionto the RN, wherein the selected precoder is indirectly selected based onthe received at least one sounding reference signal.

According to a seventh aspect of embodiments herein, the object isachieved by a method performed by a RN for receiving data from awireless device. The wireless device is configured with a set ofprecoders.

In the method, the RN receives, from the wireless device, at least onesounding reference signal precoded with a respective at least oneprecoder comprised in a subset of precoders out of the set of precoders.

Further, the RN transmits, to the wireless device, a scheduling grantfor transmitting data to the RN, which scheduling grant is based on aselected one of the received at least one sounding reference signal.

Furthermore, the RN receives data from the wireless device in accordancewith the scheduling grant.

According to an eighth aspect of embodiments herein, the object isachieved by a RN for receiving data from a wireless device. The wirelessdevice is configured with a set of precoders.

The RN is configured to receive, from the wireless device, at least onesounding reference signal precoded with a respective at least oneprecoder comprised in a subset of precoders out of the set of precoders.

Further, the RN is configured to transmit, to the wireless device, ascheduling grant for transmitting data to the RN, which scheduling grantis based on a selected one of the received at least one soundingreference signal.

Furthermore, the RN is configured to receive data from the wirelessdevice in accordance with the scheduling grant.

According to a ninth aspect of embodiments herein, the object isachieved by a computer program, comprising instructions which, whenexecuted on at least one processor, causes the at least one processor tocarry out the method in the wireless device.

According to a tenth aspect of embodiments herein, the object isachieved by a computer program, comprising instructions which, whenexecuted on at least one processor, causes the at least one processor tocarry out the method in the RN.

According to an eleventh aspect of embodiments herein, the object isachieved by a carrier comprising the computer program, wherein thecarrier is one of an electronic signal, an optical signal, a radiosignal or a computer readable storage medium.

Since the wireless device determines a subset of precoders out of theset of precoders, and transmits, to the RN, at least one soundingreference signal precoded with a respective at least one precodercomprised in the subset, the RN does not need to have knowledge aboutthe antenna arrangement of the wireless device or about the codebookwhereby the freedom of implementation and the performance gain of usingbeamforming are enhanced. This results in an improved performance in thewireless communications network.

An advantage with embodiments herein is that uplink beamforming ispossible without the wireless communications network, e.g. the RN,having knowledge about the actual antenna arrangement in the wirelessdevice.

Another advantage with embodiments herein is that since the RN does notneed to know, i.e. have detailed information on, the antenna arrangementin the wireless device, flexibility regarding the implementation, inparticular of antenna arrangements, in wireless devices is provided andthe need for having a codebook optimized with a specific antennaarrangement in mind is avoided.

Yet another advantage with embodiments herein is that the RN does notneed to sound all or a large number of the possible uplink beams butonly a UE derived subset of them, i.e. a subset derived by the wirelessdevice, whereby the overhead due to a large number of sounding referencesignals is reduced. Thereby, the procedure to sound the relevantprecoders will be faster.

BRIEF DESCRIPTION OF DRAWINGS

Examples of embodiments herein are described in more detail withreference to attached drawings in which:

FIG. 1 schematically illustrates beam forming using a one-dimensionallinear antenna array;

FIG. 2 schematically illustrates an embodiment of a communicationsnetwork;

FIG. 3 is a schematic combined flowchart and signalling scheme ofembodiments of a communications network;

FIG. 4a is a flowchart depicting embodiments of a method in a wirelessdevice;

FIG. 4b is a flowchart depicting embodiments of a method in a wirelessdevice;

FIG. 4c is a flowchart depicting embodiments of a method in a wirelessdevice;

FIG. 5 is a schematic block diagram illustrating embodiments of awireless device;

FIG. 6a is a flowchart depicting embodiments of a method in a radionode;

FIG. 6b is a flowchart depicting embodiments of a method in a radionode;

FIG. 6c is a flowchart depicting embodiments of a method in a radionode; and

FIG. 7 is a schematic block diagram illustrating embodiments of a radionode.

DETAILED DESCRIPTION

Embodiments herein relate to precoder selection for wirelesscommunication.

Below, embodiments herein will be illustrated in more detail by a numberof exemplary embodiments. It should be noted that these embodiments arenot mutually exclusive. Components from one embodiment may be tacitlyassumed to be present in another embodiment and a person skilled in theart will realize how those components may be used in the other exemplaryembodiments.

As schematically illustrated in FIG. 2 embodiments herein relate to acommunications network 100, such as a wireless communications network ora cellular communications network. The communications network 100 may bean LTE network, a WCDMA network, an GSM network, any 3GPP cellularnetwork, Wimax, or any other wireless communications network or system.

The communications network 100 may comprise a core network 102, such asan LTE Core network, e.g. a System Architecture Evolution (SAE) network,a WCDMA core network, an GSM core network, any 3GPP cellular corenetwork, a Wimax core network, or any other wireless communications corenetwork or system.

The communications network 100 may also comprise a core network node104, such as an LTE core network node, a WCDMA core network node, an GSMcore network node, any 3GPP cellular core network node, a Wimax corenetwork node, or any other wireless communications core network orsystem node.

Further, the wireless communications network 100 comprises a Radio Node(RN) 106 for wireless communication with wireless devices, such as awireless device 108, when they are located within a geographical area106 a served by the radio node 106.

The radio node 106 may be a transmission point such as a radio basestation, for example an eNodeB, also denoted eNB, a Home eNodeB, or aNodeB or any other network node capable to serve a wireless device, e.g.a user equipment or a machine type communication device in a wirelesscommunications network, such as the communications network 100. In caseof device-to-device (D2D) communication, the RN 106 may be a wirelessdevice. In such embodiments, the wireless device 108 may be referred toas a first wireless device and the RN 106 may be referred to as a secondwireless device, or vice versa.

The wireless device, e.g. the wireless device 108, herein also referredto as a user equipment or UE, operates in the wireless communicationsnetwork 100. The wireless device may e.g. be a user equipment, a mobileterminal or a wireless terminal, a mobile phone, a computer such as e.g.a laptop, a Personal Digital Assistant (PDA) or a tablet computer,sometimes referred to as a surf plate, with wireless capability, or anyother radio network unit capable of communicating over a radio link inthe wireless communications network 100. Please note that the term userequipment used in this document also covers other wireless devices suchas Machine-to-Machine (M2M) devices, even though they may not have anyuser.

According to some embodiments herein, the wireless device 108 isconfigured with a set M of precoders, which set may have a size Ω,sometimes also referred to as |M|. In other words, the set may compriseΩ precoders. The precoders may sometimes be referred to as potentialprecoders, as will be explained herein. Each precoder may in someembodiments have a length N, whereas in other embodiments, N is an upperlimit for the length of the precoders. N is also the number of antennaelements, e.g. controllable antenna elements, based on the antennaconfiguration applicable for the wireless device 108. Each precoder maycorrespond to different beam directions and/or polarization states.Hence, the set of precoders or beams may be defined in, or specific to,the implementation of the wireless device 108. The quantity N may beseen as an upper limit of the actual number of physical antenna elementsparticipating in a transmission or a reception since different precodersmay comprise zero valued entries, i.e. the precoding weight for one ormore antenna elements may be set to zero for some precoders in the setof precoders. Hence only subsets of the available antenna elements maybe used in some cases which is up to the implementation of the wirelessdevice 108. A precoder that selects subsets of antenna elements maye.g., be implemented using an analog antenna switch.

The wireless device 108 further defines or determines a subset of theseprecoders, e.g. beam directions, and uplink data transmissions may bescheduled only within the defined or determined subset. The subset ofprecoders, or beam directions, may be derived autonomously in thewireless device 108. For example, the subset may be based on downlinkmeasurements and may utilize the reciprocity, e.g. the long-termreciprocity, for example regarding direction of arrival oftransmissions, between the uplink and the downlink. A Radio Node (RN)106, e.g. an eNodeB (eNB), or a second wireless device in case of D2Dcommunication, may then configure the wireless device 108 to transmitone or more, or in some embodiments more than one, sounding referencesignals weighted by different precoders, i.e. in different beams or beamdirections, in the determined subset to further determine upon whichbeam(s) to schedule uplink data transmissions.

An advantage of embodiments herein is that the RN 106 does not need toknow, i.e. have detailed information on, the antenna arrangement in thewireless device 108 which allows for more implementation flexibility inthe wireless device 108, in particular regarding the antenna arrangementin the wireless device 108, and avoids need for specifying a codebookoptimized with a specific antenna arrangement in mind. Still the RN 106may obtain uplink channel measurements of the most relevant beams fromthe wireless device 108.

A method in the communications network 100 for performing precoderselection for wireless communication between the wireless device 108 andthe RN 106 will now be described with reference to a combined flowchartand signalling scheme depicted in FIG. 3. The wireless device 108 isconfigured with a set of precoders.

Further and in accordance with some embodiments, a method in thecommunications network 100 for transmitting data from the wirelessdevice 108 to the RN 106 and for receiving the data at the RN 106 willalso be described with reference to the combined flowchart andsignalling scheme depicted in FIG. 3. As mentioned above, the wirelessdevice 108 is configured with a set of precoders. Each precoder in theset of precoders may be defined to provide a respective transmissionpattern when applied to transmission on a set of antenna elements of thewireless device 108.

The methods comprise one or more of the following actions. It should beunderstood that actions may be taken in any suitable order and thatactions may be combined.

Action 301

In some embodiments, the wireless device 108 determines a number ofprecoders to be comprised in a subset of precoders. The wireless device108 may perform this in order to limit the number of potential precodersto be comprised in the subset. By the expression “potential precoders”is meant precoders that are available for selection and transmission.

Each precoder may comprise a set of precoding weights, wherein eachprecoding weight may correspond to at least one antenna element of thewireless device 108.

Action 301 relates to Action 401 which will be described below.

Action 302

In some embodiments, wherein the wireless device 108 has determined thenumber of precoders to be comprised in the subset as mentioned in Action301 above, the wireless device 108 may transmit the determined number orinformation relating to the determined number of precoders to the RN106. This may be done to inform the RN 106 about the size of the subset.However, it should be understood that the RN 106 does not need to knowthe exact size of the subset, i.e. the exact number of precoders to becomprised in the subset. In some embodiments, the wireless device 108transmits information relating to an upper limit of the size of thesubset.

In some embodiments, Action 302 is performed after Action 304 describedbelow. In such embodiments, the wireless device 108 determines thesubset of precoders out of the set of precoders, and thereaftertransmits the determined number or information relating to thedetermined number of precoders to the RN 106. If for example, the subsetcomprises five precoders the wireless device 108 may transmit, to the RN106, the number five or information relating to the five precoders, e.g.a respective index for each precoder. However, if the subset comprisesfive precoders but only three of them are unique, the wireless device108 may transmit only information relating to the three uniqueprecoders.

Action 302 relates to Action 402 which will be described below.

Action 303

In some alternative embodiments, the RN 106 transmits the number ofprecoders to be comprised in the subset to the wireless device 108.Thus, in such embodiments, the wireless device 108 receives the numberof precoders to be comprised in the subset from the RN 106 instead ofdetermining the number itself. In other embodiments, the RN 106 maytransmit information relating to the number of precoders, e.g. arespective index for each precoder, from which information the wirelessdevice 108 may then derive the number of precoders to be comprised inthe subset.

Action 303 relates to Actions 403 and 601 which will be described below.

Action 304

The wireless device 108 determines the subset of precoders out of theset of precoders. The wireless device 108 may in some embodimentsdetermine the subset in response to the reception of the number ofprecoders to be comprised in the subset transmitted from the RN 106 orupon reception of information relating to the number of precoders to becomprised in the subset transmitted from the RN 106.

Further, as previously mentioned, the wireless device 108 may in furtherembodiments determine the subset of precoders autonomously based on e.g.downlink measurements and utilization of reciprocity, e.g. the long-termreciprocity, for example regarding direction of arrival oftransmissions, between the uplink and the downlink.

Furthermore, the precoders may be numbered to have a consecutive orderor each precoder may be assigned a respective index. The indices may beassigned by the wireless device 108. As mentioned above, the wirelessdevice may in some embodiments receive a set of indices from the RN 106to be assigned to the precoders in the subset.

Action 304 relates to Action 404 which will be described below.

Action 305

In some embodiments, the RN 106 transmits a request, to the wirelessdevice 108, for transmission of at least one Sounding Reference Signal(SRS). The RN 106 may request transmission of the at least one SRS inorder to assess the channel quality using the different correspondingprecoders used for precoding the different SRSs of the transmitted atleast one SRS. The at least one SRS may in some embodiments comprisemore than one SRS. In other words, the at least one SRS may in someembodiments comprise a plurality of sounding reference signals.

Action 305 relates to Actions 405 and 603 which will be described below.

Action 306

The wireless device 108 transmits, to the RN 106, at least one SRSprecoded with a respective at least one precoder comprised in thesubset. The wireless device 108 may transmit the at least one SRS inresponse to the request mentioned in Action 305 above. In someembodiments, where the at least one SRS comprises more than one SRS,each of the more than one SRSs is precoded with a respective one of morethan one precoders comprised in the subset. In other words, in suchembodiments, each one of the plurality of sounding reference signals isprecoded with a respective one of a plurality of precoders comprised inthe subset.

Action 306 relates to Actions 406 and 604 which will be described below.

Action 307

The RN 106 may select a precoder comprised in the subset based on thereceived at least one SRS. The precoder may be indirectly or implicitlyselected by the RN 106 selecting the SRS that was precoded with theselected precoder by the wireless device 108.

Action 307 relates to Action 605 which will be described below.

Action 308

In some embodiments, the RN 106 determines a scheduling of atransmission from the wireless device 108 to the RN 106, whichscheduling may comprise information on the selected precoder or may bebased on information relating to the selected precoder.

Action 309

In order to inform the wireless device 108 about the precoder to be usedfor a transmission to the RN 106, the RN 106 may transmit a signalindicative of a selected precoder to be used for the transmission to theRN 106, which signal is received by the wireless device 108. In someembodiments, the RN 106 may additionally or alternatively transmit, tothe wireless device 108, a scheduling grant which scheduling grant isbased on the selected precoder. The selected precoder may be indirectlyselected based on the received at least one SRS. The at least one SRSmay in some embodiments comprise more than one SRS, i.e. a plurality ofsounding reference signals. The signal indicative of the selectedprecoder may in some embodiments comprise the scheduling grant. In suchembodiments, the signal may be seen as indicative of the selectedprecoder at least in that the scheduling grant is based on the SRS thatwas precoded with the selected precoder by the wireless device 108. Thesignal may also be indicative of the selected precoder by carrying otherinformation, such as an index of the selected precoder or a numberrelated to the order by which the SRSs were transmitted by the wirelessdevice 108 and received by the RN 106, so that the order number of theSRS indicates the selected precoder to the wireless device 108.

Action 309 relates to Actions 407 and 606 which will be described below.

Action 310

In some embodiments, the wireless device 108 transmits data to the RN106 in accordance with the received scheduling grant. Thus, the wirelessdevice 108 transmits data to the RN 106 using the selected precoder.Action 310 relates to Actions 408 and 607 which will be described below.

Action 311

In some embodiments, when the wireless device 108 and the RN 106 havemoved in relation to each other or when the radio propagationenvironment has been changed, the wireless device 108 may determine thatan update of the subset of precoders is needed.

Action 311 relates to Action 409 which will be described below.

Action 312

In some embodiments, wherein the wireless device 108 has determined thatan update of the subset is needed as described in Action 311, thewireless device 108 may transmit an update request for updating thesubset of precoders to the RN 106. This may be done in order to informthe RN 106 about the update or to receive a permission or an instructionfrom the RN 106 to perform the update. This will be described in moredetail in Action 410 below.

Action 312 relates to Actions 409, 410, and 608 which will be describedbelow.

Action 313

In response to receiving the update request transmitted from thewireless device 108 as mentioned in Action 312 above, the RN 106 maytransmit an update response. In some embodiments, the update responsecomprises a permission or an instruction for the wireless device 108 toperform the update.

Action 313 relates to Actions 411 and 609 which will be described below.

Action 314

In some embodiments, as an alternative to at least one of Actions 311,312 and 313, the RN 106 may transmit, to the wireless device 108, anupdate instruction instructing the wireless device 108 to re-evaluatethe subset of precoders. For example, this may be done when the RN 106has determined that the wireless device 108 and the RN 106 have moved inrelation to each other or that the radio propagation environment hasbeen changed.

Action 314 relates to Actions 409 and 610 which will be described below.

Action 315

In response to receiving the update instruction from the RN 106, thewireless device 108 may re-evaluate the subset of precoders to determinewhether or not the subset needs to be updated. Further, the wirelessdevice 108 may transmit a re-evaluation complete message to the RN 106when the re-evaluation has been completed.

Action 315 relates to Actions 409, 610 and 611 which will be describedbelow.

Action 316

In some embodiments, the wireless device 108 updates the subset ofprecoders. The subset of precoders may in an embodiment where Action 315is performed, be updated by the wireless device 108 based on there-evaluation of the subset of precoders.

Action 316 relates to Action 412 which will be described below.

Action 317

The wireless device 108 may indicate to the RN 106 that the subset ofprecoders have been updated. In some embodiments, the wireless device108 transmits an update complete message to the RN 106 when the updateof the subset is completed, whereby the RN 106 is informed about theupdate.

Action 317 relates to Actions 412 and 611 which will be described below.

Method performed in a wireless device 108 for assisting in precoderselection for wireless communication with the RN 106, will now bedescribed with reference to flow charts depicted in FIG. 4a-4c . Thewireless device 108 is configured with a set of precoders.

Further and in accordance with some embodiments, methods performed inthe—wireless device 108 for transmitting data to the RN 106 will also bedescribed with reference to the flow charts depicted in FIG. 4a-4c . Thewireless device 108 is configured with a set of precoders. Each precoderin the set of precoders may be defined to provide a respectivetransmission pattern when applied to transmission on a set of antennaelements of the wireless device 108.

The methods comprise one or more of the following actions. It should beunderstood that actions may be taken in any suitable order and thatactions may be combined.

Action 401

In some embodiments, cf. e.g. FIG. 4c , the wireless device 108determines a number of precoders to be comprised in the subset. Aspreviously mentioned, the wireless device 108 may perform this in orderto limit the number of potential precoders to be comprised in thesubset.

Action 402

When the wireless device 108 has determined the number of precoders asmentioned in Action 401 above, the wireless device 108 may transmit, tothe RN 106, information about the determined number of precoders. Theinformation about the determined number of precoders may in someembodiments be the determined number. In other embodiments, theinformation about the number of precoders may for example be a set ofindices assigned to the precoders in the subset as described above inrelation to Action 303. Thus, the wireless device 108 may transmitinformation about the determined number of precoders to the RN 106 inorder to inform the RN 106 about the size of the subset of precoders.

The wireless device 108 may transmit the information about thedetermined number in several ways. For example the wireless device 108may transmit the information about the number in a Media Access Control(MAC) information element, in an Radio Resource Control (RRC) message,and/or by Layer 1 (L1) and/or Layer 2 (L2) signalling, for exampleexplicit L1 signalling, and/or L1/L2 control signalling, etc.

Action 402 relates to Action 602 which will be described below.

Action 403

In some embodiments, cf. e.g. FIG. 4c , the wireless device 108 may asan alternative to Action 402, receive, from the RN 106, informationabout the number of precoders to be comprised in the subset.

The wireless device 108 may receive the information about the number inseveral ways. For example the wireless device 108 may receive theinformation about the number in a MAC information element, in an RRCmessage, and/or by L1 and/or L2 signalling, for example explicit L1signalling, and/or L1/L2 control signalling, etc.

Action 403 relates to Action 601 which will be described below.

Action 404

The wireless device 108 determines a subset of precoders out of the setof precoders, cf. e.g. FIGS. 4a -4 c.

The wireless device 108 may determine the subset of precoders based on ameasurement on at least one transmission from the RN 106 to the wirelessdevice 108.

The wireless device 108 determining the subset may comprise the wirelessdevice 108 receiving at least one transmission from the RN 106 anddetermining the subset to comprise at least one precoder, which at leastone precoder gives substantially the same transmit radiated energypattern as the receive sensed energy pattern of the received at leastone transmission, i.e. to comprise at least one precoder, which at leastone precoder gives a transmit radiated energy pattern that issubstantially equal to a receive sensed energy pattern of the receivedat least one transmission. In other words, the at least one precodergives an antenna transmission pattern that corresponds to an antennareception pattern of the received at least one transmission.

The wireless device 108 may further determine the subset based onknowledge about at least one preceding subset or based on arandom-access procedure. For example, the wireless device 108 maydetermine that the subset should comprise the at least one precedingsubset or a part thereof. Further, the wireless device 108 may determinethe subset based on a random-access procedure wherein the wirelessdevice 108 has transmitted, to the RN 106, a random access preambleusing one or more precoders, either in parallel or sequentialtransmissions. Depending on a random access scheme, e.g. depending onthe details of the random access scheme, the wireless device 108 maydetermine which one of the transmissions of the preamble the RN 106responded to. Thereby, the wireless device 108 will receive knowledgeabout at least one reasonably good precoder which will be comprised inthe subset.

Additionally or alternatively, the wireless device 108 may determine thesubset by determining a first precoder from the set of precoders to beincluded in the subset, which first precoder gives a received signalquality at the RN 106 that is better than the received signal qualitygiven by the other precoders of the set and by determining a secondprecoder to be included in the subset, which second precoder isorthogonal to the first precoder. In some embodiments, the secondprecoder is close to orthogonal or substantially orthogonal to the firstprecoder. Further, a third precoder may be determined to be orthogonalto the first and second precoders, and a fourth precoder may bedetermined to be orthogonal to the second and third precoders, etc.

By the expression “orthogonal” when used herein is meant that twoprecoding vectors w₁ and w₂ are orthogonal if the inner product w₁^(*)w₂=0, wherein w^(*) (i.e. w with “superscript *”) means thecomplex-conjugate transpose of the vector w. According to someembodiments the expression “orthogonal” is herein also taken to cover“close to orthogonal” and substantially orthogonal, in which cases theinner product between the two precoding vectors may be larger than zerobut lower than a threshold value. The inner product may also be referredto as the scalar product between the two precoding vectors.

The signal quality may be a received signal quality at the RN 106. Thereceived signal quality is related to a channel quality at the RN 106.For example, if a known signal is input to a channel, then the receivedsignal quality reflects the channel quality.

In some embodiments, the wireless device 108 determining the subset mayfurther comprise the wireless device 108 determining that a precoder inthe set of precoders should be excluded from the subset based on ameasurement of an antenna impedance, a reflected antenna power and/or ofa physical interaction. In other words, the wireless device 108 maydetermine the subset by determining a non-useful precoder in the set ofprecoders based on a measurement of an antenna impedance, a reflectedantenna power and/or of a physical interaction. According to someembodiments, the wireless device 108 may utilize a proximity sensor todetermine which set of precoders or physical antennas or antennaelements that is not useful due to e.g. a physical interaction such as ablocking hand or other object or body part in physical contact with thewireless device 108. In some embodiments, the wireless device 108 usesmeasurements of the antenna impedance or reflected power to determineantenna elements that are not useful.

Action 405

In some embodiments, cf. e.g. FIG. 4c , the wireless device 108 mayreceive, from the RN 106, a request for transmission of at least onesounding reference signal by the wireless device 108. The at least onesounding reference signal may in some embodiments comprise more than onesounding reference signals. In other words, the wireless device 108 mayreceive, from the RN 106, a request for transmission of the soundingreference signal for at least one, or more than one, precoder comprisedin the subset.

The wireless device 108 may receive the request in several ways. Forexample the wireless device 108 may receive the request in a MACinformation element, in an RRC message, and/or by L1 and/or L2signalling, for example explicit L1 signalling, and/or L1/L2 controlsignalling, etc.

Action 405 relates to Action 603 which will be described below.

Action 406

The wireless device 108 transmits, to the RN 106, at least one soundingreference signal precoded with a respective at least one precodercomprised in the subset, cf. e.g. FIGS. 4a-4c . This means that each oneof the transmitted at least one sounding reference signal is precodedwith a respective one of at least one precoder comprised in the subset.

In other words, the wireless device 108 may transmit, to the RN 106, asounding reference signal for at least one precoder comprised in thesubset. The sounding reference signal may be precoded with the at leastone precoder by applying the at least one precoder to the transmissionof the sounding reference signal on a set of antenna elements of thewireless device 108.

In some embodiments, when for example the wireless device 108 comprisesdual-polarised antenna elements, the wireless device 108 may transmitthe at least one sounding reference signal by transmitting a firstsounding reference signal precoded with a specific precoder out of therespective at least one precoder in a first polarisation, andtransmitting a second sounding reference signal precoded with thespecific precoder in a second polarisation. Thereby, the RN 106 maydetermine a phase angle, e.g. in some embodiments an optimal phaseangle, of the second polarisation relative to the first polarisation. Bythe expression “optimal phase angle” is meant a phase angle thatminimizes crosstalk between the polarisations. For example, this may bethe case when the RN 106 receives beams from two different wirelessdevices using the same precoder in different polarisations but it mayalso be the case when the RN 106 receives beams from the same wirelessdevice using the same precoder in different polarisations.

The wireless device 108 may transmit the sounding reference signal byphysical layer signalling, i.e. L1 signalling, for example explicit L1signalling. The at least one sounding reference signal may in someembodiments comprise more than one sounding reference signals, each oneof the transmitted more than one sounding reference signals beingprecoded with a respective one of more than one precoders comprised inthe subset.

Action 406 relates to Action 604 which will be described below.

Action 407

As illustrated in FIGS. 4a and 4c , the wireless device 108 may receive,from the RN 106, a signal indicative of a selected precoder to be usedfor a transmission to the RN 106, wherein the selected precoder isindirectly selected based on the transmitted at least one soundingreference signal. Alternatively or in addition, as illustrated in FIGS.4b and 30 4 c, the wireless device 108 may receive, from the RN 106, ascheduling grant for transmitting data, which scheduling grant is basedon the transmitted at least one sounding reference signal. Thescheduling grant is based on the transmitted at least one soundingreference signal in that the RN 106 upon receiving the at least onesounding reference signal may select one of the at least one soundingreference signal received at the RN 106 and transmit a scheduling grantthat is adapted to the reception conditions at the RN 106 for theselected sounding reference signal. As mentioned in Action 406, thetransmitted at least one sounding reference signal is precoded with arespective at least one precoder, out of which the RN 106, by selectingone of the at least one sounding reference signal received at the RN 106indirectly also selects the precoder that was used for precoding theselected sounding reference signal, to be used for the transmission tothe RN 106. The transmitted scheduling grant may thereby also be seen tobe based on, or adapted to, the selected precoder.

By the expression “scheduling grant is based on a selected precoder” itshould be understood that the scheduling grant comprises informationrelating to the precoder the wireless device 108 should use fortransmission to the RN 106.

Further, the expressions “scheduling grant”, “scheduling”, and“scheduling assignment” may be used interchangeably herein.

For example, the wireless device 108 may receive the signal in a MACinformation element, in an RRC message, and/or by L1 and/or L2signalling, for example explicit L1 signalling, and/or L1/L2 controlsignalling, etc. The signal indicative of the selected precoder may insome embodiments comprise the scheduling grant. The at least onesounding reference signal may in some embodiments comprise more than onesounding reference signals.

Action 407 relates to Action 606 which will be described below.

Action 408

As illustrated in FIGS. 4b and 4c , the wireless device 108 transmitsdata to the RN 106 in accordance with the scheduling grant.

Action 408 relates to Action 607 which will be described below.

Action 409

In some embodiments, cf. e.g. FIG. 4c , the wireless device 108 maydetermine that an update of the subset of precoders is needed or wouldbe beneficial. This may be the case when the wireless device 108 and/orthe RN 106 have moved relative to each other or when there is a changein the radio propagation environment. In addition or alternatively, thewireless device 108 may determine that an update of the subset ofprecoders is needed or would be beneficial when a predefined orpredetermined period of time has lapsed. Thus, the subset may be updatedat periodical time intervals or at aperiodic time intervals.

In some alternative embodiments, the wireless device 108 may determinethat an update of the subset is needed or would be beneficial byreceiving an update instruction from the RN 106, which updateinstruction instructs the wireless device 108 to re-evaluate the subsetof precoders, and by re-evaluating the subset in response to receivingthe instruction. For example, this may be the case when the RN 106 hasdetermined that the radio conditions has changed, e.g. changedsubstantially. In such embodiments, when the wireless device 108 hascompleted the re-evaluation, the wireless device 108 may furthertransmit a re-evaluation complete message to the RN 106.

For example, the wireless device 108 may receive the update instructionin a MAC information element, in an RRC message, and/or by L1 and/or L2signalling, for example explicit L1 signalling, and/or L1/L2 controlsignalling, etc. Further, the wireless device 108 may receive the updateinstruction in a random access command or a handover command. The randomaccess command may in some embodiments be an initial random accesscommand.

The wireless device 108 may further transmit the re-evaluation completemessage in a MAC information element, in an RRC message, and/or by L1and/or L2 signalling, for example explicit L1 signalling, and/or L1/L2control signalling, etc.

Action 410

In some embodiments, cf. e.g. FIG. 4c , for example when the wirelessdevice 108 has determined that an update of the subset is needed asdescribed in Action 409 above, the wireless device 108 may transmit anupdate request for updating the subset of precoders to the RN 106.

The wireless device 108 may transmit the update request to the RN 106 inorder to inform the RN 106 that an update of the subset is needed orwould be beneficial. Thereby, the RN 106 may prepare for the update ofthe subset. However, the wireless device 108 may also in someembodiments transmit the update request to the RN 106 in order toreceive a permission or instruction from the RN 106 to perform theupdate of the subset. In some embodiments, the wireless device 108transmits the update request to the RN 106 so that the RN 106 maytransmit a request to the wireless device 108 to send one or moresounding reference signals for one or more precoders comprised in theupdated subset of precoders. In some embodiments the RN 106 may transmita request to the wireless device 108 to send more than one soundingreference signals for more than one precoders comprised in the updatedsubset of precoders.

The wireless device 108 may also transmit a timing indication in theupdate request. The timing indication may indicate a point in time whenthe update of the subset is to be performed or when the update of thesubset has been performed.

For example, the wireless device 108 may transmit the update request ina MAC information element, in an RRC message, by L1 and/or L2signalling, for example explicit L1 signalling, and/or L1/L2 controlsignalling, etc.

Action 410 relates to Action 608 which will be described below.

Action 411

In some embodiments, cf. e.g. FIG. 4c , the wireless device 108 mayreceive an update response from the RN 106. The update response may bereceived in response to the transmitted update request. As will bedescribed in Action 412 below, the wireless device 108 may update thesubset of precoders in response to the update response.

The update response may comprise a permission or an instruction toperform the update of the subset. The update response may also comprisea timing indication. The timing indication may indicate a point in timewhen the update of the subset is to be performed.

For example, the wireless device 108 may receive the update response ina MAC information element, in an RRC message, by L1 and/or L2signalling, for example explicit L1 signalling, and/or L1/L2 controlsignalling, etc.

Action 411 relates to Action 609 which will be described below.

Action 412

The wireless device 108 may update the subset of precoders, cf. e.g.FIG. 4 c.

In some embodiments, the wireless device 108 updates the subset inresponse to the determination mentioned in Action 409 above.

In some alternative embodiments, the wireless device 108 updates thesubset based on the re-evaluation also mentioned in Action 409 above.

Further, the wireless device 108 may indicate to the RN 106 that thesubset has been updated. Furthermore, the wireless device may alsoindicate to the RN 106 the point in time when the subset was updated. Insome embodiments, the wireless device 108 transmits an update completemessage to the RN 106 when the subset has been updated. The updatecomplete message may comprise information relating to the point in timewhen the subset was updated. For example, the wireless device 108 maytransmit the update complete message in a MAC information element, in anRRC message, by L1 and/or L2 signalling, for example explicit L1signalling, and/or L1/L2 control signalling, etc.

To perform the method for assisting in precoder selection for wirelesscommunication with the RN 106, the wireless device 108 may comprise anarrangement depicted in FIG. 5. As previously mentioned, the wirelessdevice 108 is configured with a set of precoders.

Further and in accordance with some embodiments, to perform the methodfor transmitting data to the RN 106, the wireless device 108 maycomprise an arrangement depicted in FIG. 5. As previously mentioned, thewireless device 108 is configured with the set of precoders. Further,each precoder in the set of precoders may be defined to provide arespective transmission pattern when applied to transmission on the setof antenna elements of the wireless device 108.

In some embodiments, the wireless device 108 comprises an input and/oroutput interface 500 configured to communicate with one or more wirelessdevices, one or more radio nodes, such as the RN 106, and one or morenetwork nodes. The input and/or output interface 500 may comprise awireless receiver (not shown) and a wireless transmitter (not shown).

The wireless device 108 is configured to determine, e.g. by means of adetermining module 501 being configured to determine, a subset ofprecoders out of the set of precoders. The determining module 501 may beimplemented by a processor 506 of the wireless device 108. The processor506 will be described in more detail below.

In some embodiments, the wireless device 108 is further configured todetermine, e.g. by means of the determining module 501 being configuredto determine, a number of precoders to be comprised in the subset.

The wireless device 108 may further be configured to determine, e.g. bymeans of the determining module 501 being configured to determine, thesubset of precoders based on a measurement on at least one transmissionfrom the RN 106 to the wireless device 108.

In some embodiments, the wireless device 108 is further configured todetermine, e.g. by means of the determining module 501 being configuredto determine, the subset to comprise at least one precoder, which atleast one precoder gives substantially the same transmit radiated energypattern as the receive sensed energy pattern of a received at least onetransmission from the RN 106, i.e. to comprise at least one precoder,which at least one precoder gives a transmit radiated energy patternthat is substantially equal to a receive sensed energy pattern of thereceived at least one transmission from the RN 106.

The wireless device 108 may further be configured to determine, e.g. bymeans of the determining module 501 being configured to determine, thesubset based on knowledge about at least one preceding subset or basedon a random-access procedure.

In some embodiments, the wireless device 108 is further configured todetermine, e.g. by means of the determining module 501 being configuredto determine, a first precoder from the set of precoders to be includedin the subset, which first precoder gives a received signal quality atthe RN 106 that is better than the received signal quality given by theother precoders of the set, and to determine a second precoder to beincluded in the subset, which second precoder is orthogonal to the firstprecoder.

The wireless device 108 may further be configured to determine, e.g. bymeans of the determining module 501 being configured to determine, thata precoder in the set of precoders should be excluded from the subsetbased on a measurement of an antenna impedance, a reflected antennapower and/or of a physical interaction.

In some embodiments, the wireless device 108 is further configured todetermine, e.g. by means of the determining module 501 being configuredto determine, that an update of the subset of precoders is needed orwould be beneficial.

The wireless device 108 is configured to transmit, e.g. by means of atransmitting module 502 being configured to transmit, to the RN 106, atleast one sounding reference signal precoded with a respective at leastone precoder comprised in the subset. The transmitting module 502 may beimplemented by the wireless transmitter or the processor 506 of thewireless device 108.

Further, the wireless device is configured to transmit, e.g. by means ofthe transmitting module 502 being configured to transmit, data to the RN106 in accordance with a received scheduling grant.

In some embodiments, wherein the wireless device 108 for examplecomprises dual polarised antenna elements, the wireless device 108 isconfigured to transmit, e.g. by means of the transmitting module 502being configured to transmit, to the RN 106, at least one soundingreference signal comprises further being configured to transmit a firstsounding reference signal precoded with a specific precoder out of therespective at least one precoder in a first polarisation, and totransmit a second sounding reference signal precoded with the specificprecoder in a second polarisation.

In some embodiments, when the wireless device 108 has determined thenumber of precoders to be comprised in the subset, the wireless device108 may further be configured to transmit, e.g. by means of thetransmitting module 502 being configured to transmit, to the RN 106,information about the determined number of precoders.

The wireless device 108 may further be configured to transmit, e.g. bymeans of the transmitting module 502 being configured to transmit, anupdate request for updating the subset of precoders to the RN 106. Theupdate request may be transmitted in response to the wireless device 108determining, e.g. by means of the determining module 501 beingconfigured to determine, that an update of the subset of precoders isneeded or would be beneficial. The update request may comprise or relateto a request for updating the subset of precoders. Further, the wirelessdevice 108 may be configured to transmit, e.g. by means of thetransmitting module 502 being configured to transmit, an indication tothe RN 106, which indication indicate that the subset has been updated.The indication may also indicate the point in time for the update of thesubset. The wireless device 108 may be configured to transmit, e.g. bymeans of the transmitting module 502 being configured to transmit, theindication in an update complete message.

As will be described below, the wireless device 108 may re-evaluate thesubset of precoders in response to an update instruction from the RN106. In such embodiments, the wireless device 108 may further beconfigured to transmit, e.g. by means of the transmitting module 502being configured to transmit, a re-evaluation complete message to the RN106.

The wireless device 108 may be configured to receive, e.g. by means of areceiving module 503 being configured to receive, from the RN 106, asignal indicative of a selected precoder to be used for a transmissionto the RN 106, wherein the selected precoder is indirectly selectedbased on the transmitted at least one sounding reference signal. Thereceiving module 503 may be implemented by the wireless receiver or theprocessor 506 of the wireless device 108.

Alternatively or in addition, the wireless device 108 may be configuredto receive, e.g. by means of the receiving module 503 being configuredto receive, from the RN 106, a scheduling grant for transmitting data,which scheduling grant is based on the received at least one soundingreference signal. The received scheduling grant may also be seen to bebased on, or adapted to, the selected precoder, because by selecting oneof the at least one sounding reference signal received at the RN 106,the RN 106 also indirectly selects the precoder that was used by thewireless device 108 for precoding the sounding reference signal selectedto be used by the wireless device 108 for the transmission to the RN106. The transmission may be a data transmission. The scheduling grantmay in some embodiments be comprised in or carried by the signalindicative of the selected precoder.

In some embodiments, the wireless device is further configured toreceive, e.g. by means of the receiving module 503 being configured toreceive, from the RN 106, a request for transmission of the at least onesounding reference signal by the wireless device 108.

As an alternative to determining the number of precoders to be comprisedin the subset by itself, the wireless device 108 may further beconfigured to receive, e.g. by means of the receiving module 503 beingconfigured to receive, from the RN 106, information about the number ofprecoders to be comprised in the subset.

In some embodiments, the wireless device 108 is further configured toreceive, e.g. by means of the receiving module 503 being configured toreceive, at least one transmission from the RN 106, which at least onetransmission may be used to determine the subset of precoders asmentioned above in relation to determining module 501.

In some embodiments, the wireless device 108 may further be configuredto receive, e.g. by means of the receiving module 503 being configuredto receive, an update response from the RN 106. The wireless device 108may receive the update response in response to the update requesttransmitted to the RN 106. As previously described, the update responsemay comprise a permission or an instruction to perform the update of thesubset. The update response may also comprise a timing indication. Thetiming indication may indicate a point in time when the update of thesubset is to be performed.

Further, the wireless device 108 may be configured to receive, e.g. bymeans of the receiving module 503 being configured to receive, an updateinstruction from the RN 106, which update instruction instructs thewireless device 108 to re-evaluate the subset. In some embodiments, thewireless device 108 is configured to receive the update instruction in arandom access command or a handover command. The update instruction maycomprise a timing indication. The timing indication may indicate a pointin time when the update of the subset is to be performed.

In some embodiments, the wireless device 108 is configured to update,e.g. by means of an updating module 504 being configured to update, thesubset of precoders. The updating module 504 may be implemented by theprocessor 506 of the wireless device 108.

As mentioned above, the wireless device 108 may be configured todetermine that an update of the subset of precoders is needed or wouldbe beneficial. Thus, the wireless device 108 may be configured toupdate, e.g. by means of the updating module 504 being configured toupdate, the subset in response to the determination. The wireless device108 may further be configured to update the subset in response toreceiving the update response from the RN 106 as mentioned above inrelation to the receiving module 503.

In some embodiments, the wireless device 108 may further be configuredupdate, e.g. by means of the updating module 504 being configured toupdate, the subset of precoders based on a re-evaluation of the subset.As mentioned above, the wireless device 108 may receive an updateinstruction from the RN 106, which update instruction instructs thewireless device 108 to re-evaluate the subset. Thus, the wireless device108 may re-evaluate the subset in response to the received updateinstruction.

The wireless device 108 may also comprise means for storing data. Insome embodiments, wireless device 108 comprises a memory 505 configuredto store the data. The data may be processed or non-processed dataand/or information relating thereto. The memory 505 may comprise one ormore memory units. Further, the memory 505 may be a computer datastorage or a semiconductor memory such as a computer memory, a read-onlymemory, a volatile memory or a non-volatile memory. The memory isarranged to be used to store obtained information, data, configurations,schedulings, and applications etc. to perform the methods herein whenbeing executed in the wireless device 108.

Embodiments herein for assisting in precoder selection and/ortransmitting data to the RN 106 may be implemented through one or moreprocessors, such as the processor 506 in the arrangement depicted inFIG. 5, together with computer program code for performing the functionsand/or method actions of embodiments herein. The program code mentionedabove may also be provided as a computer program product, for instancein the form of a data carrier carrying computer program code forperforming the embodiments herein when being loaded into the wirelessdevice 108. One such carrier may be in the form of an electronic signal,an optical signal, a radio signal or a computer readable storage medium.The computer readable storage medium may be a CD ROM disc or a memorystick.

The computer program code may furthermore be provided as program codestored on a server and downloaded to the wireless device 108.

Those skilled in the art will also appreciate that the receiving module503, the transmitting module 502, the determining module 501 and theupdating module 504 above may refer to a combination of analog anddigital circuits, and/or one or more processors configured with softwareand/or firmware, e.g. stored in the memory 505, that when executed bythe one or more processors such as the processors in the wireless device108 perform as described above. One or more of these processors, as wellas the other digital hardware, may be included in a singleApplication-Specific Integrated Circuitry (ASIC), or several processorsand various digital hardware may be distributed among several separatecomponents, whether individually packaged or assembled into aSystem-on-a-Chip (SoC).

Methods performed in the RN 106 for performing precoder selection forwireless communication with the wireless device 108, will now bedescribed with reference to flow charts depicted in FIG. 6a-6c . Thewireless device 108 is configured with a set of precoders. In someembodiments, the the RN 106 may have knowledge about informationrelating to the number of precoders comprised in a subset of the set ofprecoders. Further and in accordance with some embodiments, methodsperformed in the

RN 106 for receiving data from the wireless device 108, will also bedescribed with reference to the flow charts depicted in FIG. 6a-6c . Thewireless device 108 may be configured with a set of precoders. Eachprecoder in the set of precoders is defined to provide a respectivetransmission pattern when applied to transmission on a set of antennaelements of the wireless device 108. Further, the RN 106 may in someembodiments have knowledge about information relating to the number ofprecoders comprised in a subset of the set of precoders. For example,the precoders may be numbered to have a consecutive order or theprecoders may be assigned respective indices. Thus, the RN 106 may haveknowledge about information relating to the number of precoders in thesubset or about information relating to the indices assigned to theprecoders in the subset.

The methods comprise one or more of the following actions. It should beunderstood that actions may be taken in any suitable order and thatactions may be combined.

Action 601

In some embodiments, cf. FIG. 6c , the RN 106 transmits, to the wirelessdevice 108, information about a number of precoders to be comprised inthe subset.

Action 601 relates to Action 403 previously described.

Action 602

In some embodiments as an alternative to Action 601, the RN 106receives, from the wireless device 108, information about a number ofprecoders comprised in the subset.

Action 602 relates to Action 402 previously described.

Action 603

In some embodiments, cf. FIG. 6c , the RN 106 transmits, to the wirelessdevice 108, a request for transmission, by the wireless device 108, ofat least one sounding reference signal The at least one soundingreference signal may in some embodiments comprise more than one soundingreference signals.

Action 603 relates to Action 405 previously described.

Action 604

The RN 106 receives, from the wireless device 108, at least one soundingreference signal precoded with a respective at least one precodercomprised in a subset of precoders out of the set of precoders. Thismeans that each one of the received at least one sounding referencesignal is precoded, by the wireless device 108 at transmission of thesounding reference signal, with a respective one of at least oneprecoder comprised in the subset. The at least one sounding referencesignal may in some embodiments comprise more than one sounding referencesignals, each one of the received more than one sounding referencesignals being precoded, by the wireless device 108 at transmission ofthe sounding reference signal, with a respective one of more than oneprecoders comprised in the subset.

In some embodiments, when for example the wireless device 108 comprisesdual polarised antenna elements, the RN 106 may receive the at least onesounding reference signal by receiving a first sounding reference signalprecoded with a specific precoder out of the respective at least oneprecoder in a first polarisation and receiving a second soundingreference signal precoded with the specific precoder in a secondpolarisation. Thereafter, the RN 106 may determine a phase angle of thesecond polarisation relative to the first polarisation based on thereceived first and second sounding reference signals.

Action 604 relates to Action 406 previously described.

Action 605

The RN 106 may select a precoder comprised in the subset based on thereceived at least one sounding reference signal, cf. FIG. 6 c.

In some embodiments, the RN 106 indirectly selects the precoder based onthe received at least one sounding reference signal.

For example, the received at least one sounding reference signal may beassociated with a number or with an index of a respective precoderaccording to a rule known to the wireless device 108 and the RN 106.Thereby, the RN 106 may select the number or the index of the respectiveprecoder, and by means of the selected number or selected index, the RN106 indirectly selects the precoder.

The at least one sounding reference signal may in some embodimentscomprise more than one sounding reference signals. In such embodiments,the precoder may be indirectly selected based on the received more thanone sounding reference signals or based on a selected one of thereceived more than one sounding reference signals.

Action 606

In some embodiments, cf. e.g. FIGS. 6a and 6c , and in order to informthe wireless device 108 about the precoder to be used for a transmissionto the RN 106, the RN 106 transmits, to the wireless device 108, asignal indicative of a selected precoder to be used for the transmissionto the RN 106, wherein the selected precoder is indirectly selectedbased on the received at least one sounding reference signal or based onthe received more than one sounding reference signals. The transmissionto the RN 106 may be a data transmission.

Alternatively or additionally, cf. e.g. FIGS. 6b and 6c ,the RN 106 maytransmit, to the wireless device 108, a scheduling grant fortransmitting data to the RN 106, which scheduling grant is based on aselected one of the received at least one sounding reference signal ormore than one sounding reference signals. The scheduling grant may insome embodiments be comprised in or carried by the signal indicative ofthe selected precoder. The scheduling grant may be based on the receivedsignal quality of the at least one received sounding reference signal ormore than one sounding reference signals.

In some embodiments, when a plurality of sounding reference signals aretransmitted to and received by the RN 106, the RN 106 may compare therespective received signal quality of the received sounding referencesignals and select one sounding reference signal out of the receivedsounding reference signals, which selected one sounding reference signalhas a received signal quality that is better than the received signalquality of the other received sounding reference signals. In suchembodiments, the selected precoder is indirectly selected based on theselected one of the sounding reference signal.

As previously mentioned, the signal quality may be a received signalquality at the RN 106. In some embodiments the received signal qualityis referred to as a channel quality at the RN 106.

Action 606 relates to Action 407 previously described.

Action 607

The RN 106 receives data from the wireless device 108 in accordance withthe scheduling grant.

Action 607 relates to Action 408 previously described.

Action 608

The RN 106 may receive, from the wireless device 108, an update requestfor updating the subset of precoders. As previously mentioned, theupdate request may inform the RN 106 that the update is needed or wouldbe beneficial. Alternatively or in addition, the update request maycomprise a request for a permission or an instruction to perform theupdate.

Action 608 relates to Action 410 previously described.

Action 609

The RN 106 may transmit, to the wireless device 108, an update response.As previously mentioned, the update response may comprise a permissionor an instruction to perform the update of the subset. The updateresponse may also comprise a timing indication. The timing indicationmay indicate a point in time when the update of the subset is to beperformed.

Action 609 relates to Action 411 previously described.

Action 610

In some embodiments, the RN 106 transmits, to the wireless device 108,an update instruction instructing the wireless device 108 to re-evaluatethe subset. The update instruction may comprise timing informationrelating to the point in time for the update of the subset.

The RN 106 may transmit the update instruction in a random accesscommand or a handover command. The random access command may in someembodiments be an initial random access command.

Action 610 relates to Action 409 previously described.

Action 611

The RN 106 may receive, from the wireless device 108, a re-evaluationcomplete message. Further, the RN 106 may receive an update completemessage from the wireless device 108 when the updated has beencompleted. The update complete message may comprise timing informationrelating to the point in time when the update was performed.

Action 611 relates to Actions 409 and 412 previously described.

To perform the method for performing precoder selection for wirelesscommunication with the wireless device 108, the RN 106 may comprise anarrangement depicted in FIG. 7. As previously mentioned, the wirelessdevice 108 is configured with a set of precoders. In some embodiments,the the RN 106 may have knowledge about information relating to thenumber of precoders comprised in a subset of the set of precoders.

Further and in accordance with some embodiments, to perform the methodfor receiving data from the wireless device 108, the RN 106 may comprisethe arrangement depicted in FIG. 7. The wireless device 108 isconfigured with a set of precoders. Each precoder in the set ofprecoders may be defined to provide a respective transmission patternwhen applied to transmission on a set of antenna elements of thewireless device 108. Further, the RN 106 may in some embodiments haveknowledge about information relating to the number of precoderscomprised in a subset of the set of precoders.

In some embodiments, the RN 106 comprises an input and/or outputinterface 700 configured to communicate with one or more wirelessdevices, such as the wireless device 108, one or more other radio nodes,and/or one or more other network nodes. The input and/or outputinterface 700 may comprise a wireless receiver (not shown) and awireless transmitter (not shown).

The RN 106 may be configured to receive, e.g. by means of a receivingmodule 701 configured to receive, from the wireless device 108, at leastone sounding reference signal precoded with a respective at least oneprecoder comprised in a subset of precoders out of the set of precoders.The at least one sounding reference signal may in some embodimentscomprise more than one sounding reference signals, each one of thereceived more than one sounding reference signals being precoded, by thewireless device 108 at transmission of the sounding reference signal,with a respective one of more than one precoders comprised in thesubset. The receiving module 701 may be implemented by the wirelessreceiver or a processor 706 of the RN 106. The processor 706 will bedescribed in more detail below.

In some embodiments, the RN 106 may be configured to receive, e.g. bymeans of the receiving module 701 configured to receive, data from thewireless device 108 in accordance with a scheduling grant.

The RN 106 may further be configured to receive, e.g. by means of thereceiving module 701 configured to receive, a first sounding referencesignal precoded with a specific precoder out of the respective at leastone precoder in a first polarisation, and to receive, e.g. by means ofthe receiving module 701 configured to receive, a second soundingreference signal precoded with the specific precoder in a secondpolarisation, and to determine, e.g. by means of a determining module(not shown) configured to determine, a phase angle of the secondpolarisation relative to the first polarisation based on the receivedfirst and second sounding reference signals.

In some embodiments, the RN 106 may further be configured to receive,e.g. by means of the receiving module 701 configured to receive, fromthe wireless device 108, information about a number of precoderscomprised in the subset.

The RN 106 may further be configured to receive, e.g. by means of thereceiving module 701 configured to receive, from the wireless device108, an update request for updating the subset of precoders. Thewireless device 108 may transmit the update request to the RN 106 inorder to inform the RN 106 that an update of the subset is needed.Thereby, the RN 106 may prepare for the update of the subset. However,alternatively or additionally, the wireless device 108 may transmit theupdate request to the RN 106 in order to receive a permission or aninstruction from the RN 106 to perform the update of the subset. In someembodiments, the wireless device 108 transmits the update request to theRN 106 so that the RN 106 may transmit a request to the wireless device108 to send one or more sounding reference signals for one or moreprecoders comprised in the updated subset of precoders. However, itshould be understood that the RN 106 may send an update command orinstruction to the wireless device at any time, even without a priorupdate request from the wireless device 108. For example, this may bethe case, if the RN 106 has changed something it knows will affect thewireless device 108 and it does not want to wait for the wireless device108 to discover the change.

In some embodiments, the RN 106 is further configured to receive, e.g.by means of the receiving module 701 configured to receive, from thewireless device 108, a re-evaluation complete message. Thereby, the RN106 will be informed that the wireless device 108 has completedre-evaluation of the subset.

The RN 106 may be configured to transmit, e.g. by means of atransmitting module 702 configured to transmit, to the wireless device108, a signal indicative of a selected precoder to be used for atransmission to the RN 106, wherein the selected precoder is indirectlyselected based on the received at least one sounding reference signal.The transmission to the RN 106 may be a data transmission. Alternativelyor in addition, the RN 106 may be configured to transmit, e.g. by meansof the transmitting module 702 configured to transmit, to the wirelessdevice 108, the scheduling grant for transmitting data to the RN 106,which scheduling grant is based on a selected one of the received atleast one sounding reference signal. The received scheduling grant mayalso be seen to be based on, or adapted to, the selected precoder, forreasons explained above e.g. in relation to receiving module 503 of thewireless device 108. The scheduling grant may in some embodiments becomprised in or carried by the signal indicative of the selectedprecoder. The transmitting module 702 may be the wireless transmitter(not shown) or the processor 706 of the RN 106. As previously mentioned,the selected precoder may be indirectly selected based on the receivedat least one sounding reference signal.

Further, the scheduling grant may be based on the received signalquality of the received at least one sounding reference signal. Aspreviously mentioned, in some embodiments when a plurality of soundingreference signals are transmitted to and received by the RN 106, the RN106 may be configured to compare the respective received signal qualityof the received sounding reference signals and to select one soundingreference signal out of the received sounding reference signals, whichselected sounding reference signal has a received signal quality that isbetter than the received signal quality of the other received soundingreference signals. In such embodiments, the selected precoder isindirectly selected based on the selected sounding reference signal.

In some embodiments, the RN 106 may further be configured to transmit,e.g. by means of the transmitting module 702 configured to transmit, tothe wireless device 108 a request for transmission, by the wirelessdevice 108, of the at least one sounding reference signal The at leastone sounding reference signal may in some embodiments comprise more thanone sounding reference signals.

The RN 106 may further, in some embodiments, be configured to transmit,e.g. by means of the transmitting module 702 configured to transmit, tothe wireless device 108, information about a number of precoders to becomprised in the subset.

In some embodiments, the RN 106 may further be configured to transmit,e.g. by means of the transmitting module 702 configured to transmit, tothe wireless device 108, an update response.

Further, the RN 106 may be configured to transmit, e.g. by means of thetransmitting module 702 configured to transmit, to the wireless device108, an update instruction instructing the wireless device 108 tore-evaluate the subset. The RN 106 may be configured to transmit, e.g.by means of the transmitting module 702 configured to transmit, theupdate instruction in a random access command or a handover command.

The RN 106 may be configured to select, e.g. by means of a selectingmodule 703 configured to select, a precoder comprised in the subsetbased on the received at least one sounding reference signal. Theselecting module 703 may be implemented by the processor 706 of the RN106.

In other words, the precoder is indirectly selected based on thereceived at least one sounding reference signal or based on a selectedone of the received at least one sounding reference signal. The at leastone sounding reference signal may in some embodiments comprise more thanone sounding reference signals. In such embodiments, the precoder may beindirectly selected based on the received more than one soundingreference signals or based on a selected one of the received more thanone sounding reference signals.

The RN 106 may be configured to schedule, e.g. by means of a schedulingmodule 704 configured to schedule, one or more transmissions from thewireless device 108 to the RN 106 based on the indirectly selectedprecoder. The scheduling module 704 may be implemented by the processor706 of the RN 106.

The RN 106 may also comprise means for storing data. In someembodiments, the RN 106 comprises a memory 705 configured to store thedata. The data may be processed or non-processed data and/or informationrelating thereto. The memory 705 may comprise one or more memory units.Further, the memory 705 may be a computer data storage or asemiconductor memory such as a computer memory, a read-only memory, avolatile memory or a non-volatile memory. The memory is arranged to beused to store obtained information, data, configurations, schedulings,and applications etc. to perform the methods herein when being executedin the RN 106.

Embodiments herein for performing precoder selection for wirelesscommunication with the wireless device 108 and/or for receiving datafrom the wireless device 108 may be implemented through one or moreprocessors, such as the processor 706 in the arrangement depicted inFIG. 7, together with computer program code for performing the functionsand/or method actions of embodiments herein. The program code mentionedabove may also be provided as a computer program product, for instancein the form of a data carrier carrying computer program code forperforming the embodiments herein when being loaded into the RN 106. Onesuch carrier may be in the form of an electronic signal, an opticalsignal, a radio signal or a computer readable storage medium. Thecomputer readable storage medium may be a CD ROM disc or a memory stick.

The computer program code may furthermore be provided as program codestored on a server and downloaded to the RN 106.

Those skilled in the art will also appreciate that the transmittingmodule 702, the receiving module 701, the selecting module 703, and thescheduling module 704 above may refer to a combination of analog anddigital circuits, and/or one or more processors configured with softwareand/or firmware, e.g. stored in the memory, that when executed by theone or more processors such as the processors in the RN 106 perform asdescribed above. One or more of these processors, as well as the otherdigital hardware, may be included in a single Application-SpecificIntegrated Circuitry (ASIC), or several processors and various digitalhardware may be distributed among several separate components, whetherindividually packaged or assembled into a System-on-a-Chip (SoC).

Some Exemplifying Embodiments

According to some exemplifying embodiments, a set M of precoders that isspecific for the wireless device 108 is defined and stored in e.g. amemory of the wireless device 108. In other words, each wireless device108 has its own specific set of precoders which may be stored in amemory of the wireless device 108. In the general case, each precoderdefines a complex number for each of the N antenna elements of thewireless device 108. Mathematically, if the wireless device 108 has Nantenna elements, a precoder may be represented as the vector, w:w=[w ₀ w ₁ . . . w _(N−2) w _(N−1)]wherein w_(i) is a complex number representing the phase and amplitudeadjustment of the signal at antenna element i. Note that some antennaelements in this precoding vector may be zero, indicating that theassociated antenna element is disabled. The set M of precoders is thusthe collection of the available precodersM={w ⁽⁰⁾ , . . . w ^((Ω−1))}

Hence, each precoder w in the set may correspond to a directive beamaccording to the phase coherent beamforming theory according tobackground art which may be generalized to arbitrary arrays. Note that aprecoder may also be designed to achieve a radiation pattern for whichhigh directivity is not the primary design target. It may be useful ifsome precoders in the set have approximately omni-directional radiationpattern and different precoders are used to achieve polarizationdiversity.

A feature of some embodiments herein is that the set M of precoders inthe wireless device 108 need not be known to the communications network,e.g. the RN 106. It is thus up to each manufacturer of wireless devicesto optimize the set depending on the antenna arrangement of therespective wireless device. Hence, different wireless device in thecommunications network may have different sets M of precoders stored ina memory. This is useful since the set M of precoders may be optimizedfor each type of wireless device, whether it is a handset, a laptop, atablet or a phablet etc.

Different wireless device form factors, such as e.g. cell phone, tablet,laptop, stationary access point etc., imply different antenna placementsand thus different sets M of precoders. With the set M of precodersdefined for a wireless device, it is observed that the set M ofprecoders may be much larger than the uplink sounding capacity of thecommunications network. Hence, the number of precoders of the set M maybe in the range of tens to hundreds. It is thus impractical in realityto transmit sounding reference signal for each possible precoding vectorin the set M since each sounding occasion consumes uplink bandwidth andpower. On the other hand, it is beneficial to have a large set M to copewith many different channel conditions. It is thus a challenge how todeal with the conflicting interests of a large set M of precoders anduplink sounding capacity.

In some embodiments herein, the basic scheme to acquire uplink channelstate information at the communications network, e.g. the RN 106, maythus be described in the following actions:

-   -   1. A subset S∈M of interesting precoders (e.g. beams) out of the        set M of possible precoders (e.g. beams) may be determined in        the wireless device 108. Enumeration of the precoders (e.g.        beams) in S may be performed in such a way that each precoder        (beam) in S has a unique identifier, e.g. by numbering the        precoder (e.g. beams) from 0 to |S|−1. This relates to e.g.        Actions 301, 302, 304, 401, 402, and 404 described above.        -   a. The selected subset S may thus be given by S={w^((k) ⁰ ⁾,            . . . w^((k) ^(X−1) ⁾}        -   wherein k₀, . . . , k_(X−1) are the indices of the selected            precoding vectors.    -   2. The RN 106 may request a sounding reference signal of one or        more of the beam directions in the subset S in order to assess        the channel quality using the different corresponding precoders.        However, it should be understood that this action may be        optional and that the RN 106 may schedule data transmissions on        different precoders (e.g. beams) in the subset S without a        preceding sounding reference signal. This relates to e.g.        Actions 305, 405 and 603 described above.    -   3. The RN 106 may schedule data transmission on one or more of        the precoders (e.g. beams) in the subset S. A scheduler of the        RN 106, e.g. the scheduling module 704, may use the estimated        uplink channel quality from action 2 above in the scheduling        process, e.g. to determine the transport block size and        modulation and coding scheme.

Thus, although the wireless device 108 may be capable of forming up to|M| different beams since this is the total size of the set M ofpossible precoders, only X=|M| of these precoders may be visible to theRN 106. Especially, the RN 106 does not need to know how the wirelessdevice 108 derived the subset S. Thus, the RN 106 does not need to haveknowledge about the antenna arrangement in the wireless device 108.However, the wireless device 108 must use the same enumeration of beamsin the subset S in all the actions 1-3 mentioned above. That is, if acertain precoder (beam) in the set M in action 1 above is referred to asprecoder (beam) number i, sounding reference signals and uplinkscheduling in actions 2 and 3, respectively, must be able to refer tothe same precoder (beam) by the index i.

The size |S| of the subset S may either be fixed in the specifications,configurable to the wireless device 108 by the RN 106 using higher layersignaling, such as RRC signaling, or determined by the wireless device108 itself. In the latter case, the wireless device 108 may need toagree on the size with the RN 106 for example by simply reporting itsconclusion to the RN 106. The wireless device 108 may need to agree onthe size with the RN 106 so both the wireless device 108 and the RN 106knows in which range valid precoder indices are when for examplerequesting sounding. Combinations of the three methods of setting thesize ISI of the subset S may also be envisioned.

In some embodiments, the size of the subset S is signaled in thesounding request message to the wireless device 108. Hence, the RN 106may indicate to the wireless device 108 to transmit X sounding referencesignals. Then the wireless device 108 may make the selection of thesubset S out of the possible M precoders.

Determining the subset S of transmit precoding weights in action 1 maybe done in multiple ways. For example, the wireless device 108 may relyon reciprocity between uplink (UL) and downlink (DL), such as at leastlong term reciprocity, and measure the downlink quality in all thebeams. For example, by finding or determining the receive precoderweights and then finding or determining the transmit precoder weightsfrom the subset S or set M that gives essentially the same radiationpattern, i.e. that gives a transmit radiation pattern that isessentially equal to or corresponding to the receive sensitivity patternobtained with the determined receive precoder weights, and selecting theISI best receive ones as members of the transmit precoder subset S. Thewireless device 108 may also use prior knowledge of the most promisingbeam directions from preceding subsets S or a previous random-accessstep. This relates to e.g. Actions 304 and 404 described above.

The subset S of transmit precoding weights may change over time, e.g. ifthe wireless device 108 due to e.g. mobility or other changes in thepropagation environment has concluded that a different set of beams isof better quality. Hence, the wireless device 108 may need to repeat thedetermination of the subset according to action 1 above with someperiodicity or triggered by some event. Such event may be an internalevent in the wireless device 108, e.g. based on measurements, but mayalso be an external explicit request from the communications network,e.g. the RN 106. This relates to e.g. Actions 312, 409 and 610 describedabove.

Since the enumeration of the beams in subset S in the three differentactions 1-3 above needs to be kept, the wireless device 108 may notupdate the subset S autonomously. Different possibilities to handle thisexist but at least the following two tools may be useful:

-   -   The wireless device 108 may, when detecting that updating the        subset S is beneficial, transmit an ‘update request’ to the RN        106. The wireless device 108 may either wait for an ‘update’        response from the RN 106 before it updates the subset S or the        wireless device 108 may update the subset without waiting for a        the response. In some embodiments, the former is more preferable        than the latter. In the latter case there is a risk that uplink        data transmissions not yet effectuated but scheduled by the RN        106 based on the old subset S may fail. This relates to e.g.        Actions 312, 313, 316, 409, 410, 411, 412, 608, and 609.    -   The RN 106 may transmit an update command or instruction to the        wireless device 108, which update command may request the        wireless device 108 to reevaluate or re-determine the subset S.        Either the wireless device 108 may respond with a ‘reevaluation        complete’ response or the forming of a new subset S is assumed        to be completed a predefined time from reception of the        ‘reevaluation request’ command. This relates to e.g. Actions        314, 315, 411, 610 and 611 described above.

Other procedures in the wireless device 108 may also imply forming of anew subset S. Examples hereof are random access, e.g. initial randomaccess, and handover commands.

In some embodiments, the selection of the subset S is performed by firstfinding the best precoding vector from the set M, w^((k) ⁰ ⁾. Then anorthogonal or close to orthogonal vector from this vector w^((k) ⁰ ⁾ isfound as a second vector in the subset S, w^((k) ¹ ⁾. Hence,

w^((k₀)^(*))w^((k₁)) ⪡ 1

assuming these vectors are normalized. This criterion avoids the problemthat the wireless device 108 selects two precoding vectors that arenearly parallel, which is likely in an unrestricted algorithm, since ifw^((k) ⁰ ⁾ is the best candidate then a near parallel second vector islikely also a good candidate. The algorithm may then continue to find athird candidate which is orthogonal or close to orthogonal to theprevious two selected ones and so on. This relates to e.g. Action 404described above.

Further, in some embodiments, it is assumed that dual polarized antennasare used at the wireless device 108 and that the wireless device 108transmits one or more sounding reference signals in such way that the RN106 may determine a desired phase angle, e.g. the optimal phase angle,of a second polarization relative to the first polarization. This may beachieved as follows. For each precoder in the set S, the wireless device108 uses the precoder twice, one for each polarization, in the soundingreference signal transmission. Hence the RN 106 may then measure therelative phase between the two polarization branches, when this precoder(i.e. beam) is used. It is assumed that the RN 106 knows that thewireless device 108 uses this sounding technique when dual polarizedantennas are used at the wireless device 108. This capability may beindicated by the wireless device 108 to the RN 106 using for example RRCconfiguration and capability signaling. In other words, the wirelessdevice 108 may be configured to indicate this capability to the RN 106using for example RRC configuration and capability signaling and the RN106 may be configured to receive sounding reference signals from awireless device 108 using dual polarized antennas when the wirelessdevice 108 has indicate this capability to the RN 106. When this is thecase, the wireless device 108 is scheduled to transmit soundingreference signals for X beams/precoders but the wireless device 108actually transmits 2X sounding reference signals to achieve the dualpolarized channel sounding. This relates to e.g. Action 406 describedabove.

When using the word “comprise” or “comprising” it shall be interpretedas non-limiting, i.e. meaning “consist at least of”. Further, when usingthe word “a”, or “an” herein it should be interpreted as “at least one”,“one or more”, etc.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appended claims.

The invention claimed is:
 1. A method performed by a wireless device forassisting in precoder selection for wireless communication with a RadioNode (RN), the method comprising: determining, in the wireless device, asubset of precoders out of a set of precoders configured in the wirelessdevice and unknown to the RN; and transmitting, to the RN, at least onesounding reference signal precoded with a respective at least oneprecoder comprised in the subset.
 2. The method of claim 1, furthercomprising: receiving, from the RN, a signal indicative of a selectedprecoder to be used for a transmission to the RN, wherein the selectedprecoder is indirectly selected from the subset of precoders based onthe transmitted at least one sounding reference signal.
 3. The method ofclaim 2, wherein the signal indicative of a selected precoder carries ascheduling grant for transmitting data to the RN, which scheduling grantis based on the transmitted at least one sounding reference signal, themethod further comprising: transmitting data to the RN in accordancewith the scheduling grant.
 4. The method of claim 1, further comprising:receiving, from the RN, a request for transmission of the at least onesounding reference signal by the wireless device.
 5. The method of claim1, wherein transmitting the at least one sounding reference signalcomprises: transmitting a first sounding reference signal precoded witha specific precoder out of the respective at least one precoder in afirst polarization; and transmitting a second sounding reference signalprecoded with the specific precoder in a second polarization.
 6. Themethod of claim 1, further comprising: determining a number of precodersto be comprised in the subset; and transmitting, to the RN, informationabout the determined number of precoders.
 7. The method of claim 1,further comprising: receiving, from the RN, information about a numberof precoders to be comprised in the subset.
 8. The method of claim 1,wherein determining the subset further comprises: determining the subsetof precoders based on a measurement on at least one transmission fromthe RN to the wireless device.
 9. The method of claim 1, whereindetermining the subset further comprises: receiving at least onetransmission from the RN; and determining the subset to comprise atleast one precoder, which at least one precoder gives substantially thesame transmit radiated energy pattern as the receive sensed energypattern of the received at least one transmission.
 10. The method ofclaim 1, wherein determining the subset further comprises: determiningthe subset based on knowledge about at least one preceding subset orbased on a random-access procedure.
 11. The method of claim 1, whereindetermining the subset further comprises: determining a first precoderfrom the set of precoders to be included in the subset, which firstprecoder gives a received signal quality at the RN that is better thanthe received signal quality given by the other precoders of the set; anddetermining a second precoder to be included in the subset, which secondprecoder is orthogonal to the first precoder.
 12. The method of claim 1,wherein determining the subset further comprises: determining that aprecoder in the set of precoders should be excluded from the subsetbased on a measurement of an antenna impedance, a reflected antennapower and/or of a physical interaction.
 13. The method of claim 1,further comprising: determining that an update of the subset ofprecoders is needed; and updating the subset in response to thedetermination.
 14. The method of claim 13, wherein updating the subsetfurther comprises: transmitting an update request for updating thesubset of precoders to the RN in response to the wireless devicedetermining that an update of the subset of precoders is needed.
 15. Themethod of claim 14, wherein updating the subset further comprises:receiving an update response from the RN, wherein the updating of thesubset is performed by the wireless device in response to receiving theupdate response from the RN.
 16. The method of claim 13, whereindetermining that an update of the subset is needed further comprises:receiving an update instruction from the RN instructing the wirelessdevice to re-evaluate the subset of precoders; re-evaluating the subset;and wherein the updating the subset further comprises: up-dating thesubset based on the re-evaluation.
 17. The method of claim 16, whereindetermining that an update of the subset is needed further comprises:transmitting a re-evaluation complete message to the RN.
 18. The methodof claim 16, wherein the update instruction is received in a randomaccess command or a handover command.
 19. A method performed by a RadioNode (RN) for performing precoder selection for wireless communicationwith a wireless device, the method comprising: receiving, from thewireless device, at least one sounding reference signal precoded with arespective at least one precoder comprised in a subset of precoders outof a set of precoders configured in the wireless device and unknown tothe RN; and transmitting, to the wireless device, a signal indicative ofa selected precoder to be used for a transmission to the RN, wherein theselected precoder is indirectly selected from the subset of precodersbased on the received at least one sounding reference signal.
 20. Themethod of claim 19, wherein the signal indicative of the selectedprecoder carries a scheduling grant for transmitting data to the RN,which scheduling grant is based on a selected one of the received atleast one sounding reference signal, the method comprising: receivingdata from the wireless device in accordance with the scheduling grant.21. The method of claim 19, further comprising: transmitting, to thewireless device a request for transmission, by the wireless device, ofthe at least one sounding reference signal.
 22. The method of claim 19,wherein receiving the at least one sounding reference signal comprises:receiving a first sounding reference signal precoded with a specificprecoder out of the respective at least one precoder in a firstpolarization; receiving a second sounding reference signal precoded withthe specific precoder in a second polarization; and determining a phaseangle of the second polarization relative to the first polarizationbased on the received first and second sounding reference signals. 23.The method of claim 19, wherein the scheduling grant is based on thereceived signal quality of the received at least one sounding referencesignal.
 24. The method of claim 19, further comprising: receiving, fromthe wireless device, information about a number of precoders comprisedin the subset.
 25. The method of claim 19, further comprising:transmitting, to the wireless device, information about a number ofprecoders to be comprised in the subset.
 26. The method of claim 19,further comprising: receiving, from the wireless device, an updaterequest for updating the subset of precoders.
 27. The method of claim26, further comprising: transmitting, to the wireless device, an updateresponse in response to the update request.
 28. The method of claim 19,further comprising: transmitting, to the wireless device, an updateinstruction instructing the wireless device to re-evaluate the subset.29. The method of claim 28, further comprising: receiving, from thewireless device, a re-evaluation complete message.
 30. The method ofclaim 28, wherein the update instruction is transmitted in a randomaccess command or a handover command.
 31. A wireless device forassisting in precoder selection for wireless communication with a RadioNode (RN), the wireless device being configured to: determine a subsetof precoders out of a set of precoders configured in the wireless deviceand unknown to the RN; and transmit, to the RN, at least one soundingreference signal precoded with a respective at least one precodercomprised in the subset.
 32. The wireless device of claim 31, thewireless device further being configured to: receive, from the RN, asignal indicative of a selected precoder to be used for a transmissionto the RN, wherein the selected precoder is indirectly selected from thesubset of precoders based on the transmitted at least one soundingreference signal.
 33. The wireless device of claim 32, the wirelessdevice being configured to: receive, from the RN, the signal indicativeof a selected precoder carrying a scheduling grant for transmitting datato the RN, which scheduling grant is based on the transmitted at leastone sounding reference signal; and transmit data to the RN in accordancewith the scheduling grant.
 34. The wireless device of claim 31, thewireless device further being configured to: receive, from the RN, arequest for transmission of the at least one sounding reference signalby the wireless device.
 35. The wireless device of claim 31, wherein thewireless device being configured to transmit, to the RN, at least onesounding reference signal comprises the wireless device being furtherconfigured to: transmit a first sounding reference signal precoded witha specific precoder out of the respective at least one precoder in afirst polarization; and transmit a second sounding reference signalprecoded with the specific precoder in a second polarization.
 36. Thewireless device of claim 31, the wireless device further configured to:determine a number of precoders to be comprised in the subset; andtransmit, to the RN, information about the determined number ofprecoders.
 37. The wireless device of claim 31, the wireless devicefurther configured to: receive, from the RN, information about a numberof precoders to be comprised in the subset.
 38. The wireless device ofclaim 31, wherein the wireless device being configured to determine asubset of precoders comprises the wireless device being furtherconfigured to: determine the subset of precoders based on a measurementon at least one transmission from the RN to the wireless device.
 39. Thewireless device of claim 31, wherein the wireless device beingconfigured to determine a subset of precoders comprises the wirelessdevice being further configured to: receive at least one transmissionfrom the RN; and determine the subset to comprise at least one precoder,which at least one precoder gives substantially the same transmitradiated energy pattern as the receive sensed energy pattern of thereceived at least one transmission.
 40. The wireless device of claim 31,wherein the wireless device being configured to determine a subset ofprecoders comprises the wireless device being further configured to:determine the subset based on knowledge about at least one precedingsubset or based on a random-access procedure.
 41. The wireless device ofclaim 31, wherein the wireless device being configured to determine asubset of precoders comprises the wireless device being furtherconfigured to: determine a first precoder from the set of precoders tobe included in the subset, which first precoder gives a received signalquality at the RN that is better than the received signal quality givenby the other precoders of the set; and determine a second precoder to beincluded in the subset, which second precoder is orthogonal to the firstprecoder.
 42. The wireless device of claim 31, wherein the wirelessdevice being configured to determine a subset of precoders comprises thewireless device being further configured to: determine that a precoderin the set of precoders should be excluded from the subset based on ameasurement of an antenna impedance, a reflected antenna power and/or ofa physical interaction.
 43. The wireless device of claim 31, thewireless device further configured to: determine that an update of thesubset of precoders is needed; and update the subset in response to thedetermination.
 44. The wireless device of claim 43, wherein the wirelessdevice being configured to update the subset comprises the wirelessdevice being further configured to: transmit an update request forupdating the subset of precoders to the RN in response to the wirelessdevice determining that an update of the subset of precoders is needed.45. The wireless device of claim 44, wherein the wireless device beingconfigured to update the subset comprises the wireless device beingfurther configured to: receive an update response from the RN, whereinthe subset is updated by the wireless device in response to receivingthe update response from the RN.
 46. The wireless device of claim 43,wherein the wireless device being configured to determine that an updateof the subset is needed comprises the wireless device being furtherconfigured to: receive an update instruction from the RN instructing thewireless device to re-evaluate the subset; re-evaluate the subset; andbeing configured to update the subset by being further configured to:up-date the subset based on the re-evaluation.
 47. The wireless deviceof claim 46, wherein the wireless device being configured to determinethat an update of the subset is needed comprises the wireless devicebeing further configured to: transmit a re-evaluation complete messageto the RN.
 48. The wireless device of claim 46, the wireless devicebeing further configured to receive the update instruction in a randomaccess command or a handover command.
 49. A Radio Node (RN) forperforming precoder selection for wireless communication with a wirelessdevice, the RN being configured to: receive, from the wireless device,at least one sounding reference signal precoded with a respective atleast one precoder comprised in a subset of precoders out of a set ofprecoders configured in the wireless device and unknown to the RN; andtransmit, to the wireless device, a signal indicative of a selectedprecoder to be used for a transmission to the RN, wherein the selectedprecoder is indirectly selected from the subset of precoders based onthe received at least one sounding reference signal.
 50. The RN of claim49, the RN being configured to: transmit, to the wireless device, thesignal indicative of the selected precoder carrying a scheduling grantfor transmitting data to the RN, which scheduling grant is based on aselected one of the received at least one sounding reference signal; andreceive data from the wireless device in accordance with the schedulinggrant.
 51. The RN of claim 49, the RN being further configured to:transmit, to the wireless device, a request for transmission, by thewireless device, of the at least one sounding reference signal.
 52. TheRN of claim 49, the RN being configured to receive the at least onesounding reference signal by being further configured to: receive afirst sounding reference signal precoded with a specific precoder out ofthe respective at least one precoder in a first polarization; receive asecond sounding reference signal precoded with the specific precoder ina second polarization; and determine a phase angle of the secondpolarization relative to the first polarization based on the receivedfirst and second sounding reference signals.
 53. The RN of claim 50,wherein the scheduling grant is based on the received signal quality ofthe received at least one sounding reference signal.
 54. The RN of claim49, the RN being further configured to: receive, from the wirelessdevice, information about a number of precoders comprised in the subset.55. The RN of claim 49, the RN being further configured to: transmit, tothe wireless device, information about a number of precoders to becomprised in the subset.
 56. The RN of claim 49, the RN being furtherconfigured to: receive, from the wireless device, an update request forupdating the subset of precoders.
 57. The RN of claim 56, the RN beingfurther configured to: transmit, to the wireless device, an updateresponse.
 58. The RN of claim 49, the RN being further configured to:transmit, to the wireless device, an update instruction instructing thewireless device to re-evaluate the subset.
 59. The RN of claim 58, theRN being further configured to: receive, from the wireless device, are-evaluation complete message.
 60. The RN of claim 58, the RN beingfurther configured to transmit the update instruction in a random accesscommand or a handover command.